1. Field of the Invention
The present invention relates to a clutch operator arrangement for introducing an actuating force into a friction clutch.
2. Description of the Related Art
DE 195 47 081 A1 has disclosed an actuating device for a clutch, in which a clutch operator arrangement has two ramp regions which can rotate with respect to one another about an axis of rotation, follow one another in the axial direction and between which rolling bodies designed in the form of balls are positioned. If one of the components which have ramp surfaces is driven in rotation, for example by being driven by a Bowden cable, the ramp surfaces which lie axially opposite one another move, with a rolling movement of the balls, with the result that the two components are shifted axially with respect to one another and a clutch release force is generated.
EP 0 478 427 A1 also discloses an arrangement of this type, in which associated groups of ramp surfaces, with dedicated ball elements between them, can move with respect to one another in order to generate the axial thrust force.
One drawback of these known clutch operator mechanisms which operate using pairs of ramp surfaces which lie opposite one another is that, on account of the ramp surface pairings which follow one another in the circumferential direction, the circumferential angle sector over which ramp surfaces of this nature can extend is restricted, primarily also because a plurality of ball elements of this nature have to be distributed in the circumferential direction in order to achieve uniform axial force transmission or generation. To generate a predetermined axial movement on the output side, therefore, a relatively large ramp pitch is required, and this in turn requires relatively high input forces in order ultimately to be able to work against the force of a force accumulator.
Furthermore, clutch operator mechanisms which operate, for example, with a clutch release lever or with piston/cylinder systems arranged concentrically with respect to the axis of rotation are known, but these systems are comparatively large and often undesirable.
The object of the present invention is to provide a clutch operator arrangement which, while being of small overall size and of simple structural design, is able to generate high actuating forces.
According to the invention, this object is achieved by the fact that the clutch operator arrangement comprises a ball screw arrangement.
Ball screws are used, for example, in machine tools in order to convert rotary movements into linear translation movements. The present invention makes use of the fact that, ultimately, the ball screws do not have the rotation angle limitation which is present in the prior art. It is therefore possible, even with a relatively small input force, to generate relatively high actuating forces, by means of which the force accumulators used in friction clutches, such as for example diaphragm springs, can be acted on and actuated. A further significant advantage of ball screws of this type is that they are able to transmit forces in both axial directions, so that they can be used with both pulled and pushed clutches, without having to make design changes to the basic structure of the region which converts the rotational movement into the translational movement.
By way of example, it is possible to provide for the ball screw arrangement to comprise a spindle element, which on an outer circumferential surface has a first groove arrangement, a nut element, which surrounds the spindle element and on its inner circumferential surface has a second groove arrangement, a plurality of ball elements, at least some of which engage in the first groove arrangement and the second groove arrangement, the spindle element being rotatable about an axis of rotation with respect to the nut element and, in the event of rotation of the spindle element with respect to the nut element about the axis of rotation, the ball elements which engage in the first groove arrangement and the second groove arrangement, by rotating about a respective ball axis of rotation, rolling along the first groove arrangement and the second groove arrangement, and for one element out of the nut element and the spindle element to be or be able to be supported on a substantially stationary assembly, the friction clutch to be or be able to be acted on by the other element out of the nut element and spindle element, and at least one element out of the nut element and the spindle element to be able to be driven to rotate about the axis of rotation, in order to produce a relative displacement between the spindle element and the nut element in the direction of the axis of rotation.
According to a first alternative design variant, a drive arrangement which engages on that element out of the nut element and the spindle element which is intended to act on the friction clutch, in order to set this element in rotation about the axis of rotation, may be provided for the purpose of generating the translational movement.
Such a design variant of the drive arrangement may, for example, be provided if the spindle element is fixed, on the substantially stationary assembly, against rotation about the axis of rotation and movement in the direction of the axis of rotation, and if the nut element can be driven to rotate about the axis of rotation by means of the drive arrangement.
Since, in an arrangement of this type, the drive arrangement ultimately engages on the element which moves in translation in the axial direction, i.e. the nut element, it is necessary to ensure that the drive arrangement is also able to follow this translational movement. In an embodiment which is very simple to implement, it is possible to provide for the drive arrangement to comprise a cable pull element which engages on the nut element. Alternatively, however, it is possible for the drive arrangement to comprise a drive slide element, preferably a drive lever element, which interacts with the nut element for rotational movement driving in an interaction region.
In a further alternative design variant of the clutch operator arrangement according to the invention, it is possible to provide a drive arrangement which engages on that element out of the nut element and the spindle element which is intended to be supported on the substantially stationary assembly, in order to set this element in rotation about the axis of rotation. This variant has the advantage that the drive arrangement, through interaction with an assembly which is substantially stationary in the axial direction, does not have to follow a translational movement. In an embodiment of this nature it is possible, for example, to provide for the spindle element to be mounted on the substantially stationary assembly so as to rotate about the axis of rotation, while it substantially cannot be displaced in the direction of the axis of rotation, and for the nut element to be held in such a way that it can be displaced in the direction of the axis of rotation but substantially cannot rotate about the axis of rotation. To prevent the nut element from also executing a corresponding rotational movement in the event of rotation of the spindle element, it is furthermore possible to provide a rotational-movement blocking arrangement, by means of which the nut element is connected to the substantially stationary assembly in such a manner that it can move in the axial direction and is stopped from rotating about the axis of rotation.
In this embodiment, the drive arrangement may have a toothed element, preferably a rack element, which meshes with mating toothing, preferably outer circumference toothing, provided on the spindle element.
Furthermore, the ball screw arrangement according to the invention is preferably designed in such a manner that the first groove arrangement has at least one first thread, preferably with a plurality of turns, that the second groove arrangement has at least one second thread assigned to each first thread of the first groove arrangement, the at least one second thread preferably having at least one turn, the turn end regions of which are connected to one another via a ball-return section.
In order to minimize the frictional forces which occur when carrying out an actuating movement, it is proposed for the other element out of the nut element and the spindle element to engage on the friction clutch, preferably a force accumulator thereof, by means of a bearing arrangement.
As has already been stated above, it is possible, depending on whether use with a pulled clutch or with a pushed clutch is desired, for the other element to act on the friction clutch with an actuating force which is directed substantially away from the stationary assembly or to act on the friction clutch with an actuating force which is directed substantially toward the stationary assembly. In this case, there is preferably also an action element which, based on the direction of the actuating force, engages behind an element which is acted upon, preferably a force accumulator, of the friction clutch and is releasably coupled to the other element out of the nut element and the spindle element. In this way, it is ensured that even producing the pulling interaction between the other element out of the nut element and the spindle element and, for example, the force accumulator can be achieved in a simple way, yet at the same time it is possible to dismantle the system, for example in order to carry out maintenance work.
As has already been mentioned above, it is an object, with actuating systems of this type, in which it is necessary to work against relatively high forces, to keep the friction losses occurring in the system itself as low as possible. An inherent characteristic of ball screws is that the ball elements which serve to transmit force interact with the spindle element and the nut element at regions of these elements which are at different radial distances from the axis of rotation. The result is that, for a predetermined rotation angle of the ball elements about their associated ball axes of rotation, the ball elements on the element which lies further toward the outside, namely the nut element, which has a longer rolling path, would have to move further than on the rolling path of the spindle element. In reality, in use this ultimately leads to the balls slipping in places, with corresponding friction losses. To counteract this problem, it is proposed for, based on the ball axes of rotation, an effective ball-rolling radius with which the ball elements roll along the first groove arrangement to be smaller than an effective ball-rolling radius with which the ball elements roll along the second groove arrangement.
The provision of a smaller effective ball-rolling radius for interaction with the first groove arrangement, i.e. the groove arrangement provided on the spindle element, now ensures that, when the balls are executing a rotary movement about their associated ball axes of rotation, they can actually cover a shorter rolling distance on the first groove arrangement than on the second groove arrangement. In this way, it is possible to substantially avoid the occurrence of sliding friction in the region of these surface regions which interact by rolling.
By way of example, it is possible to provide for the ball elements to be able to roll along a first rolling-surface region of the first groove arrangement and a second rolling-surface region of the second groove arrangement, while rotating about the respective ball axis of rotation, and for, at least during the rolling movement, the ball elements to be in contact with the first rolling-surface region by means of a first ball-surface region which is at a shorter distance from the ball axis of rotation than a second ball-surface region, by means of which the ball elements are in contact with the second rolling-surface region at least during the rolling movement.
To be able to achieve this different manner of interaction between the ball elements and the different groove arrangements, it is proposed, for example, for the first groove arrangement to have a groove cross-sectional profile with a first surface curvature radius in the region of the first rolling-surface region, for the second groove arrangement to have a groove cross-sectional profile with a second surface curvature radius in the region of the second rolling-surface region, and for the first surface curvature radius to be smaller than the second surface curvature radius. Furthermore, it is possible for the first groove arrangement and the second groove arrangement to have a respective groove cross-sectional profile with a surface curvature radius which decreases from an opening region toward a groove base.
According to a further preferred embodiment of the clutch operator arrangement according to the invention, it is possible to provide for the surface curvature radius of the first groove arrangement and/or the surface curvature radius of the second groove arrangement in the region of the groove base to be smaller than the radius of the ball elements. In this way, it is ensured that, irrespective of the state of load, the ball elements cannot reach the base of the groove. The result is that in the region of the groove base there is a region of the volume of the groove arrangements which is never used by the ball elements, so that dust which ultimately collects in this region cannot contribute to any significant deterioration in the rolling properties.
The present invention also relates to a friction clutch in which a clutch operator arrangement according to the invention is provided. Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.